Continuous furnaces are used for a variety of applications, such as the manufacture of electronic components. These furnaces often have a set of thermal or heating chambers within each of which the temperature and composition of the atmosphere are controlled. Product is advanced sequentially through each chamber at a determined rate to achieve a desired thermal and atmosphere profile.
Product may be advanced through continuous furnaces in various manners, for example, in one type of continuous furnace, the product sits on a metal mesh belt which pulls the product through the furnace. In another type, a continuous pusher furnace, the product is placed on plates or carriers or boats that are pushed into the entrance of the furnace. Each subsequent plate pushes the plate in front of it. A line of contacting plates is advanced by pushing on the rearmost plate in the line. Often, it is desirable to operate two chambers within a continuous furnace at different atmospheres that must be kept separated. Typically, the chambers are spaced by tunnels or vestibules. Often doors at the entrance and exit of the chambers are provided to retain the atmosphere within the chamber. These doors, however, are costly and complex. To close the door in a continuous pusher furnace, product carriers in a contacting line must be separated, for example, by pushing the carrier at the head of the line at 90.degree. to move it off the line of travel and into a purge chamber or furnace section. A door is then closed behind the isolated carrier and the chamber purged. The carrier may be advanced to the next chamber by another pusher along a line offset from the first line. This procedure must be repeated for each carrier. This requires additional furnace length, cost, and multiple pushers.